The present invention relates generally to a clamping mechanism for opening and closing a mold. Specifically, the present invention relates to a toggle-type linkage mechanism for opening and closing two halves of a mold of the type employed on an extrusion blow molding wheel.
Conventional extrusion blow molding apparatuses have typically comprised a wheel mounted on a rotating shaft with a plurality of molds positioned on the wheel about the shaft for rotating the plurality of molds past an extrusion die located adjacent to the wheel and extruding a continuous parison. Each mold typically included two mold halves each comprising a mold cavity half therein so that when the mold halves were closed the mold defined a mold cavity corresponding to the configuration of the article to be molded, such as a container. Blow molding with such an extrusion blow molding apparatus entailed rotating the wheel to move each mold, seriatim, past the extrusion die with the mold halves in an open configuration and closing the mold halves of each mold around the parison to enclose the parison within the mold. The apparatus then inserted a blowing needle into the parison within the closed mold and introduced internal pressure to the parison forcing it to inflate and conform to the configuration of the mold cavity. The molded object was then cooled and the mold opened to release the molded object from the mold.
The opening and closing of each pair of mold halves was typically controlled by a pneumatic, hydraulic or electrically driven mold clamp in which the mold halves were placed. The mold clamp consisted of a two halves, one each associated with one of the mold halves. The drive force necessary for holding the mold clamps closed was dictated by the separation force exerted on the molds by the blow air employed to inflate the parison(s) within the mold cavity. As is understood by those of ordinary skill in the art, larger molds comprised a larger surface area and typically created a larger separation force. Molds accepting multiple parisons similarly faced increased separation force based, in part, on the overall surface area of the mold and the type of mold clamp employed. A clam shell type mold clamp, as is known to those in the art, pivotally connected the two mold clamp halves at one end so that one or both of the mold clamp halves were pivoted about the pivotal connection to open and close the molds. The separation force exerted by the blow air on a clam shell type mold clamp created a separation moment about the pivotal connection of the mold clamp halves. When the clam shell type mold clamp was employed with multiple cavity molds designed to accept multiple parisons, standard physics dictated that the separation force on the mold cavity furthest from the clam shell clamp pivotal connection created a greater separation moment than mold cavity located closer to the pivotal connection; given mold cavities of identical configuration. Sufficient clamping force had to be applied to the mold clamp in order to prevent mold separation.
Typically, however, the larger clamping force necessary to counteract the large separation forces or moments created by some clamping apparatuses dictated large expensive mechanical, hydraulic, pneumatic or electrical systems capable of producing and maintaining high forces. These larger systems were often slower in response time. There is therefore a need for an improved mold clamp drive mechanism for extrusion blow molding apparatuses.
Accordingly, it is an object of the present invention to provide a wheel type extrusion blow molding machine having a mold clamp drive apparatus capable of generating a high clamp force.
It is a further object of the invention to provide a wheel type extrusion blow molding machine having a small and efficient mold clamp drive apparatus capable of generating a high clamp force.
It is another object of the invention to provide a wheel type extrusion blow molding machine having a clamp drive apparatus employing mechanical advantage to efficiently generate a high clamp force from relatively modest forces provided to the clamp drive apparatus.
It is yet another object of the invention to provide a wheel type extrusion blow molding machine having a clamp drive apparatus that holds the mold clamps together during blow molding while imposing a relatively small portion of the mold separation forces on the drive of the clamp drive apparatus.
It is an additional object of the present invention to provide a wheel type extrusion blow molding machine that relieves the necessity of a locking mechanism to absorb forces being exerted on the clamp drive apparatus during blow molding.
It is a further object of the present invention to provide a wheel type extrusion blow molding machine having a mold clamp drive apparatus capable of generating a high clamp force for a clam shell type mold clamp.
It is still a further object of the invention to provide a wheel type extrusion blow molding machine having a small and efficient mold clamp drive apparatus capable of generating a high clamp force for a clam shell type mold clamp.
It is another object of the invention to provide a wheel type extrusion blow molding machine having a clamp drive apparatus employing mechanical advantage to efficiently generate a high clamp force for a clam shell type mold clamp from modest forces provided to the clamp drive apparatus.
It is yet another object of the invention to provide a wheel type extrusion blow molding machine having a clamp drive apparatus for a clam shell type mold clamp that substantially locks the mold clamps together during blow molding and relieves the necessity of substantial force being provided to the clamp drive apparatus during blow molding.
The above objects and other objects and features of the invention will be readily appreciated by one of ordinary skill in the art from the following detailed description of the preferred embodiment for carrying out the invention when taken in connection with the following drawings.